Recent estimates indicate that 10% to 12% of 1 - and 2-year-olds suffer from mental health problems that warrant intervention. Yet, the majority of infants and toddlers with social-emotional/behavioral problems do not receive any mental health services. This unmet need occurs despite recent legislation (IDEA, 1997) requiring state early intervention programs to provide services for problems in social-emotional development and arises, in part, from limitations in measures that have been available for assessing social-emotional problems and competencies in infants and toddlers. The work proposed in this application will examine the clinical validity of two parent-report measures of social-emotional problems and competencies in 1- and 2-year-old children: (1) a screener, the Brief Infant-Toddler Social and Emotional Assessment (BITSEA); and (2) a longer measure, the Infant-Toddler Social & Emotional Assessment (ITSEA). These measures assess internalizing, externalizing, regulatory, maladaptive and atypical problems, as well as social-emotional competence. In an earlier study, both the BITSEA and ITSEA (B/ITSEA) demonstrated solid test-retest and inter-rater reliability. Preliminary support for their validity comes from their associations with other parent-report measures and from observational ratings of child problem behaviors. However, to improve critically needed early identification and intervention efforts, it is crucial to establish their validity in identifying and characterizing clinically significant problems. In the proposed study, the B/ITSEA will be validated against consensus psychiatric diagnostic status and observational assessments of parent-child interactions in a clinic-referred sample (N~200) and a sociodemographically matched comparison sample (N~200). The primary goals of the proposed work are to evaluate the validity of: (1) the B/ITSEA in identifying children with any consensus social-emotional diagnosis; (2) the major ITSEA domains (i.e., internalizing, externalizing and dysregulation) in identifying children with disorders in specific domains; (3) the B/ITSEA in detecting parent-child relational disturbances and (4) the ITSEA Competence domain. Once validated, the BITSEA and ITSEA will facilitate screening and early intervention efforts, as well as research endeavors to characterize the early course of social-emotional and behavior problems in both general and clinical populations.